A light-emitting diode composed of aluminum nitride (AlN), gallium nitride (GaN), indium nitride (InN), or a mix crystal thereof emits light in a wide wavelength region from ultraviolet to infrared by adjusting the composition of the film included in the light-emitting diode. Non-patent Document 1 discloses a commercially-available light-emitting diode which emits visible light.
FIG. 13 shows a cross-sectional view of the light-emitting diode composed of a nitride semiconductor disclosed in Patent Document 1.
As shown in FIG. 13, the light-emitting diode comprises a low-temperature growth buffer layer 92 consisted of GaN, an n-type GaN cladding layer 93, a multi-quantum well layer 94, a p-type GaN cladding layer 95, a window electrode layer 96, and a p-side electrode 97 on a sapphire substrate 91 having a surface direction of (0001) in this order.
The window electrode layer 96 comprises both of a function of diffusing current extensively and a function of transparence for extracting light outside. An example of the material of the window electrode layer 96 is tin-doped indium oxide (ITO). An n-side electrode 98 is formed on the n-type GaN cladding layer 93.
Patent Documents 2 and 3 disclose a light-emitting diode composed of a nitride semiconductor.
Patent Document 4 discloses a light-emitting diode comprising a transparent electrode consisted of a ZnO layer.
Patent Document 5 discloses a method for fabricating a ZnO single-crystal used as a transparent electrode by liquid-phase epitaxy method.
Patent Document 6 discloses a light-emitting diode comprising a plurality of optical components having a shape of an inverted taper.